Animation ended callback

Is there a design reason that the current SpatialTranslator and KeyframeController implementations do not seem to include any sort of "I've finished" callback?  Is it a performance thing (arbitrary processing in what should just be a spatial update region), or has nobody gotten to it?

Aside from myself, is there any desire for such a thing? 

I am standing for the same problem, I think I will have to extend KeyframeController for my purpose and check every update if a specific animation has "ended".